The present disclosure relates generally to the field of contrast and/or color contrast control in displays. More particularly, the present disclosure relates to color contrast control and/or contrast control of a see-through display.
See-through displays are utilized in a wide variety of applications including but not limited to medical, military, avionic, entertainment, sporting, navigation and computing applications. In one exemplary application, see-through displays are used in head-up display (HUD) systems and wearable displays, such as, helmet mounted display (HMD) systems, etc. Other see-through displays include, but are not limited to, augmented reality displays and digital night vision systems.
In aircraft applications, HUD and HMD systems advantageously allow the flight crew to maintain eye contact with the outside environment while simultaneously viewing information from aircraft systems and sensors in a graphical and alphanumeric format overlaying the outside world view on a computer. Head-up display systems are known to provide conformal information such that displayed features overlay the environmental view. The display features can include display information from a camera or other imaging sensor (such as a visible light imaging sensor, infrared imaging sensor, millimeter wave radar imager, etc.) mounted on the aircraft.
The contrast and color contrast of display symbology and images viewed on see-through displays, such as HUDs, HMDs, digital night vision systems and augmented reality displays, can be adversely affected by the ambient illumination as seen through the display. In see-through display systems that include a combiner or combining optics, the ambient illumination is generally provided through the combiner or combining optics. Bright ambient light can adversely affect the contrast associated with an image projected on the combiner. Further, colors can be washed out when the display symbology or display image matches the color of the ambient illumination, thereby making the display symbology or display image difficult to ascertain. For example, a red symbol can be washed out when viewed at sunset, especially a sunset that provides a reddish glow to the atmosphere.
The color balance of images on the see-through display can also be affected by ambient light. Changes to the color balance change the overall mixture of colors associated with the image on the color display. Color balance changes can make the image and symbology appear less visually pleasing, and less accurate, and can obscure display symbology and images.
Generally, see-through display systems utilize manual display brightness control or an automatic brightness control (ABC) algorithm to compensate for varying ambient light conditions. The ABC algorithm generally utilizes a single photo detector directed toward the see-through view and provides brightness adjustment based upon ambient light received at a single point. The photo detector can only represent a point in the general direction of ambient light and does not take into account the detailed content of the see-through view. Accordingly, the ABC algorithm provides a global adjustment to display brightness based upon a very limited view of ambient light conditions.
Digital night vision systems are see-through displays that can also have problems associated with mixed ambient conditions. For example, mixed urban environments may contain areas that are lit by street lights and viewable with the naked eye and other areas such as darkened alleys which are only viewable using the sensors. In conventional digital night vision systems, the sensor enhances the entire scene, even parts of the scene that can already been seen by the naked eye. Enhancement of the entire mixed scene potentially can degrade the user's view of the outside world because the view from the naked eye can be better than the view through the sensor when the outside scene is viewable. (The resolution of the digital night vision system or sensor is typically far less than the user's visual acuity in lighted conditions). Thus, objects that are visible can actually be degraded if viewed through the conventional night vision system.
Accordingly, there is a need for a system for and a method of color contrast and/or contrast control for a see-through display. There is also a need for a contrast control for see-through displays that compensates for the detailed content of the see-through view and provides a more specific adjustment to display contrast or color contrast. Further still, there is a need for a system for and a method of adjusting display contrast in a more sophisticated fashion. Further still, there is a need for a system for and a method of adjusting color contrast in color displays viewed against the outside world. Further still, there is a need for a system for and a method of providing a display of mixed visible and sensor enhanced/sensed images. Further still, there is a need for a see-through display that provides a sensor overlay of mixed visible and sensor-enhanced/sensed objects. Further still, there is a need for a system for and a method of operating night vision equipment which allows the user to see more easily images that are viewable with the naked eye as well as images that are viewable using the sensor.